What Is the Combined DNA Index System (CODIS)?

The Combined DNA Index System, known as CODIS, is the FBI-run network of databases that lets crime laboratories across the United States store forensic DNA profiles and automatically compare them against samples from other jurisdictions. As of November 2025, the system holds more than 19 million profiles from convicted offenders and over 6 million from arrestees, and it has assisted in more than 758,000 investigations.¹ A DNA profile developed at a county lab can be searched against samples nationwide, and the software runs those comparisons on its own.

How the System Is Organized

CODIS is built in three tiers. Local crime laboratories run the Local DNA Index System (LDIS), where profiles are first developed from evidence and offender samples. Those profiles move up to the State DNA Index System (SDIS), which is the central repository for every participating lab in that state and controls what gets forwarded to the top tier. At the top sits the National DNA Index System (NDIS), which the FBI maintains under 34 U.S.C. § 12592.²

Each tier adds a layer of quality review. By the time a profile reaches NDIS, it has passed checks at the lab that produced it, at the state administrator level, and at the federal level. That is how a profile uploaded in one state becomes searchable against evidence from every other participating state.

What Kinds of Profiles CODIS Holds

The system separates profiles by source, which is what makes matching useful. The main categories are:

Convicted Offender Index — DNA from people found guilty of qualifying offenses. This is the largest category, with over 19.2 million profiles.¹
Arrestee Index — DNA from people arrested for offenses that qualify under the applicable law. Which offenses qualify varies by jurisdiction. Over 6.1 million profiles.¹
Forensic Index — DNA developed from crime scene evidence left by an unknown person, such as blood, saliva, or skin cells. Roughly 1.45 million profiles.¹
Missing Persons Indexes — DNA from unidentified human remains and from relatives who voluntarily submit samples to help locate missing family members.

Splitting known-person profiles from unknown-source profiles is what generates useful leads. A hit between the Forensic Index and the Convicted Offender Index points to a specific person. A hit between two Forensic Index entries tells investigators the same unknown person left evidence at two different scenes.

One boundary worth noting: elimination samples do not go into CODIS. When crime scene evidence contains DNA from someone who is not a suspect, such as a consensual partner or the victim, laboratories may collect a voluntary sample from that person to filter their DNA out of the analysis. Only the remaining unknown DNA is uploaded. If a later elimination sample turns out to match a forensic profile already in the database, that forensic profile must be removed.

What a CODIS Profile Actually Contains

A CODIS profile is not a full genetic readout. Laboratories use Short Tandem Repeat (STR) analysis to examine specific locations, called loci, on the DNA strand. Those loci sit in non-coding regions, so they reveal nothing about a person’s health, appearance, ancestry, or any other trait. What gets stored is essentially a string of numbers representing the alleles found at each locus, along with an agency identifier and a specimen number. No names, Social Security numbers, or other personal identifiers are held at the national level.³

Since January 2017, CODIS has required analysis at 20 core STR loci.⁴ Convicted offender, arrestee, and legal profiles must include results at all 20. Forensic profiles from crime scenes must attempt all 20 but can be uploaded with as few as 8 of the original core loci, provided the profile has a match rarity of at least one in ten million.³ The lower threshold for forensic profiles reflects the reality that crime scene samples are often degraded or mixed.

Who Has to Give a DNA Sample

Federal collection authority comes from 34 U.S.C. § 40702, which lets the Attorney General collect DNA from people arrested, facing charges, or convicted of qualifying federal offenses, and from non-U.S. persons detained under federal authority. The Bureau of Prisons must collect a sample from every person in its custody convicted of a qualifying federal offense, and federal probation offices have the same duty for people on federal probation, parole, or supervised release.⁵

Refusing to cooperate is a Class A misdemeanor under the same statute, and federal authorities may use reasonable force to collect a sample. If your DNA is already on file, agencies are not required to take a new sample, but they can.⁵

State rules vary. Every state requires collection from people convicted of felonies, but states differ on whether they also collect from those convicted of misdemeanors, from arrestees before conviction, or from juveniles adjudicated for certain offenses. The DNA Fingerprint Act of 2005 expanded federal authority to reach people merely arrested or detained under federal authority, not just those convicted.⁶

How Matches Are Made

Once a profile passes quality checks and enters NDIS, searches run automatically. The system compares newly uploaded and modified profiles Monday through Friday, and missing-persons records are searched at least monthly.⁷ No analyst has to trigger a comparison manually.

Two kinds of results come out of that process. An offender hit occurs when a crime scene profile matches someone in the Convicted Offender or Arrestee Index, giving investigators a name. A forensic hit links two or more crime scenes to each other, showing that the same unknown person left DNA at multiple locations. Forensic hits are useful even without identifying the person, because they let investigators combine cases and share leads.

A hit is a lead, not evidence of guilt. When the software flags a match, it sends an electronic notification to each submitting laboratory, and a confirmation workflow begins. The labs verify data accuracy and exchange case details. Investigators then review the full case file, determine which specific piece of evidence produced the match, decide whether further testing is needed, and evaluate other evidence supporting the lead. A second investigator typically reviews the case before it moves toward prosecution. No law enforcement action is taken on an unverified hit.

How CODIS Differs From Genetic Genealogy

CODIS is often confused with the investigative genetic genealogy that has driven several high-profile cold case arrests. They are separate systems that never share data. CODIS stores STR profiles: short numerical strings from non-coding DNA that identify a person but reveal nothing else. Genetic genealogy uses single-nucleotide polymorphism (SNP) testing, which produces a much broader genetic picture that can trace family lineages through commercial databases such as GEDmatch. The Department of Justice’s interim policy requires investigators to exhaust CODIS searching before turning to genealogy databases.⁸

Because genealogy searching requires a type of DNA analysis that FBI laboratories do not perform, the crime scene sample must be sent to a private vendor. The resulting profile is then compared against public genealogy databases containing profiles from people who voluntarily submitted their DNA.⁸ For anyone worried about genetic privacy: giving a DNA sample through the criminal justice system does not put your data on an ancestry site, and uploading your DNA to a genealogy service does not put it in CODIS.

Getting a Profile Removed

Profiles are not necessarily permanent. Federal law requires participating laboratories to expunge qualifying profiles from NDIS in specific circumstances. For convicted offenders, a profile must be removed if the lab receives a certified copy of a court order showing the conviction has been overturned. For arrestees, expungement is required if charges were dismissed, resulted in acquittal, or were never filed within the applicable time period.³

For records arising from a federal conviction or an arrest under federal authority, the individual or their attorney submits a written request to the FBI Laboratory Division at Quantico, Virginia, along with a certified copy of the final court order. The order must be signed by a judge, dated, and include enough identifying information (at minimum, full name and Social Security number or date of birth) to confirm the person’s identity. Without a certified court order, the FBI will not process the request.⁹

This federal process covers only records from federal or District of Columbia cases. If your DNA record stems from a state conviction or arrest, contact the relevant state agency. State databases operate under their own laws and procedures.⁹ Getting a state charge dismissed does not automatically pull your profile from NDIS. You have to affirmatively request removal through the correct agency with the correct paperwork.

Privacy Rules and Penalties for Misuse

Access to CODIS data is tightly restricted. Disclosure of stored samples and analyses is limited to criminal justice agencies for identification purposes, judicial proceedings where the evidence is otherwise admissible, criminal defendants who have a right to access evidence in their own cases, and anonymized statistics for research and quality control.³

Penalties for misuse are set out in 34 U.S.C. § 12593. Someone with authorized access to individually identifiable DNA information in a federal law enforcement database who knowingly discloses it to an unauthorized recipient faces a fine of up to $100,000. Someone who obtains such information without authorization faces a fine of up to $250,000, up to one year in prison, or both.¹⁰

The most fundamental privacy protection is baked into the data itself. A CODIS record is a set of numbers at 20 STR loci plus an agency code and a specimen number. It cannot tell anyone what a person looks like, what diseases they carry, or who their relatives are. Even if the raw data were exposed, it would reveal almost nothing about the person behind it.³

1
FBI Law Enforcement. CODIS-NDIS Statistics
2
Office of the Law Revision Counsel. 34 USC 12592 – Index to Facilitate Law Enforcement Exchange of DNA Identification Information
3
Federal Bureau of Investigation. CODIS and NDIS Fact Sheet
4
FBI Law Enforcement. CODIS Archive
5
Office of the Law Revision Counsel. 34 USC 40702 – Collection of DNA Samples
6
Congress.gov. S 1606 – DNA Fingerprint Act of 2005
7
FBI Law Enforcement. NDIS Operational Procedures Manual
8
United States Department of Justice. Department of Justice Announces Interim Policy on Emerging Method to Generate Leads for Unsolved Violent Crimes
9
Federal Bureau of Investigation. DNA Fingerprint Act of 2005 Expungement Policy
10
Office of the Law Revision Counsel. 34 USC 12593 – Federal Bureau of Investigation